Filament structure having arc suppressing means



May 19, 1970 J. A. RANDMER ET L 13,

F'ILAMENT STRUCTURE HAVING ARC SUPPRESSING MEANS Filed Dec. 7, 1967 uvvewrons v I I .mcoa A. RA/VDMER 4e ER/Cl-l 0. PETER FIG. 3 W

- A ENT United States Patent US. Cl. 313-278 4 Claims ABSTRACT OF THE DISCLOSURE A filament support structure for an electron tube comprising a linear array of parallel, U-shaped, filament wires extending longitudinally in an axial plane of the tube, a crossbar at the bight end of the filaments having extension tabs which grazingly touch the opposed sides of the bight ends of the filaments at the midpoints and a wire connected to the bight ends of the filaments and attached at each end to the crossbar.

Background of the invention This invention relates to an electrode structure for electron discharge tubes and is concerned more particularly with a means for maintaining alignment of the filaments which avoids intermittent contact between the filament wires and the aligning structure.

In some types of power tubes, the cathode structure comprises a linear array of parallel filament wires extending longitudinally in an axial plane of the tube. Often, the filament strands in the aforementioned power tubes are U-shaped, having one end connected to a cathode terminal of the tube, through a common supporting memher, and the other end connected to another cathode terminal of the tube through another common supporting member. The two common supporting members are usually insulatingly attached to each other and are commonly called support decks. The high density electron emission required for power tube applications is obtained by passing a filament current through the U-shaped wires and heating them to an incandescent state. When heating up to this condition, the filament strands undergo thermal expansion, and, consequently, elongate in the longitudinal plane of the filament structure. Any lateral movement of the filament wires toward the closely adjacent grid structure alters the electrical characteristics of the tube, and contact with the grid electrode itself results in catastrophic failure of the tube. Therefore, the bight ends of the U-shaped filament wires must be allowed to move longitudinally but must be restrained from moving laterally toward the grid.

A structural member at the distal end of the U-shaped filaments can be provided with tabs that just grazingly touch the sides of the bight ends of the filaments at the midpoint. Thus, the filament wires can be restrained from moving laterally while expanding longitudinally during the operation of the tube. However, it has been found that the midpoints of all the U-shaped filaments contacted by the structural member are not at the same potential. In theory, equal lengths of filament wire have the same value of resistance and will have the same voltage drop for a given value of current. Therefore, the midpoint of the U-shaped filament wires being equidistant from the support decks, should be equipotential. However, in practice, it has been found that equal lengths of filament wire do not always have the same value of resistance. Because of the large value of current flowing through the filaments of these power tubes, the differences in resistance for equal lengths of filament wire show up as significant diiferences in potential at the midpoints of the U-shaped filaments. Since the structural member which restrains lateral movement of the filaments connects points of potential difference, equalization currents flow through the structural member between the points of potential difference. Such equalization currents are tolerable as long as they are steady and do not overheat the connecting structural member.

When a power tube having the described filament structure is subjected to shock or vibration, the bight ends of the U-shaped filaments make and break contact with the structural member and, thereby, interrupt and reestablish the equalization currents flowing through the connecting crossbar. One result of making and breaking contact with the structural member is the generation of electrical noise in the associated circuitry. Another result of the interruption and reestablish-ment of equilization currents is the production of minute arcing between the intermittent contacting members. The arcing can affect the potential differences between the electrodes of the tube and can cause material from the filament wires or the restraining tabs to be vaporized and redeposited on other tube structures. The deposition of this material on the grid or the plate can be in the form of whisker growths which will become points of highly concentrated voltage potentials. These high potential points on the grid or plate can seriously alter the electrical characteristics of the tube and can cause arcing between electrodes which will lead to voltage breakdown of the tube. Furthermore, this deposi tion of metal on dielectric members of the t-ubes structure can degrade the insulating properties of these members. The problem is to connect the filament wires to the restraining structural member so that equalization currents will not be interrupted and, at the same time, allow the filaments to expand longitudinally while restraining lateral movement toward the grid.

Summary of the invention A linear array of parallel, U-shaped filament wires hangs freely in an axial plane of the tube to permit unrestricted longitudinal expansion of the filaments during the operation of the tube. A crossbar located at the bight end of the U-shaped filament wires has extension tabs which grazingly touch the opposed sides of the filament wires at the midpoints of the closed filament ends to restrain lateral movement while permitting longitudinal movement of the filaments. A wire is connected to the midpoints of the closed filament ends and attached at each end to the crossbar, thus maintaining steady contact between the crossbar extension tabs and the midpoints of the closed filament ends. The steady contact, even during shock and vibration of the tube, will prevent interruption of the equalization currents and avoid arcing between the filament wires and the extension tabs of the crossbar.

Brief description of the drawings For a better understanding of this invention, reference is made to the drawings wherein:

FIG. 1 is a fragmentary axial sectional view of a tube embodying the invention;

FIG. 2 is an enlarged, fragmentary view of the means used to insulatingly support the crossbar feature of the invention;

FIG. 3 is an enlarged fragmentary elevational view partly in section showing the interconnection of the closed ends of the filaments to the crossbar;

FIG. 4 is a enlarged, fragmentary sectional view taken on line 44 of FIG. 1.

Description of the preferred embodiment Referring to the drawing, wherein like characters of reference designate like parts throughout the several views,

a tube embodying the invention is shown in FIG. 1 with the grid and anode electrodes removed for purposes of clarity. The tube comprises a gas-tight envelope closed at one end by a metallic anode cup (not shown), preferably made of copper material. The open end of the anode cup is hermetically attached to one end of a dielectric cylinder 11, preferably ceramic, which is similarly attached at the other end to grid terminal 13 by means of Kovar sleeve 12. Another dielectric cylinder 15, preferably ceramic, is hermetically attached at one end to the opposite'side of grid terminal 13 by means of Kovar sleeve 14 and is similarly attached at the other end to one side of cathode terminal ring 17, preferably copper, by means of Kovar sleeve 16. Still another dielectric cylinder 19 is hermetically attached to the opposite side of cathode terminal ring 17 by means of Kovar sleeve 18 and is similarly attached at the other end to one side of annular cathode terminal 21, preferably copper, by means of Kovar sleeve 20. An exhaust tubulation 22, preferably copper, is circumferentially attached to the central aperture in annular cathode terminal 21 and is sealed off after processing of the tube is completed.

Within the gas-tight envelope just described, a coaxial support cylinder (not shown), preferably copper, connects cathode terminal 21 to an oblong support deck 31, and a concentric support cylinder (not shown), preferably copper, connects cathode terminal 17 to another oblong support deck 32. The two support cylinders are insulatingly spaced from each other and from the surrounding gastight envelope. For purposes of rigidity and alignment, support decks 31 and 32 are insulatingly attached to each other by conventional means with the use of dielectric bushings and washers (not shown). Grid terminal 13 extends radially inward and is attached to one end of a tubular support member 23, preferably copper, which terminates at the other end in two parallel shoulders 24, one on each side of the oblong support decks 31 and 32 and insulatingly spaced therefrom. The grid electrode (not shown) comprises two frames of parallel, metal rods, one attached to each shoulder 24, which extend longitudinally in planes parallel with and closely adjacent to the plane of the filament structure.

Parallel connecting rods 33 are attached to support decks 31 and 32 by conventional means, such as brazing, for example, and extend longitudinally in a plane centrally located between grid support shoulders 24. The connecting rods 33 attached to support deck 31 pass insulatingly through holes 34 in support deck 32 and terminate in the same transverse plane as the connecting rods 33 attached to support deck 31. Two metallic support rods 35, one adjacent each end of oblong support deck 32, have one end attached to support deck 32 by conventional means, such as brazing, and extend longitudinally in an axial plane of the tube. The respective support rods 35, preferably molybdenum, have a reduced diameter at the other end, as shown more clearly in FIG. 2, thus forming respective shank portions 36 and shoulders 37. Dielectric sleeves 38, preferably ceramic, slidingly engage respective shank ortions 36 and abut the annular surfaces of respective shoulders 37. A crossbar 46 which spans the intervening space between support rods 35 is provided with two apertures 47, one adjacent each end of crossbar 46. The periphery of each aperture 47 encircles the shank portion 36 of a support rod 35 and is insulated therefrom by the raised portion 39a on the adjacent end of respective dielectric bushings 39, preferably ceramic. Dielectric bushings 39 slidingly engage the shank portion 36 of respective support rods 35 and are supported in place by cap nuts 40, preferably molybdenum, which are press-fitted onto the reduced diameter end of respective support rods 35. Thus, crossbar 46 is uniformly spaced a predetermined distance from connecting rods 33 and insulated from the support rods 35 which are connected to support deck 32.

The ends of parallel, U-shaped filament wires 48 are attached to the distal ends of connecting rods 33 by conventional means, such as welding or brazing. Each U- shaped filament wire 48 has one end attached to a connecting rod 33 that extends from support deck 31 and the other end attached to a connecting rod 33 that extends from support deck 32. The resulting linear array of parallel filament wires 48 hangs longitudinally in the same axial plane as that of the supporting rods 35. As shown more clearly in FIG. 4, crossbar 46 has a U-shaped cross section, elongated in places where opposing tabs 49 extend from the side walls of the crossbar 46. The closed or bight ends of respective U-shaped filament wires 48 extend longitudinally into the open end of the U-shap-ed cavity formed by crossbar 46 and extension tabs 49. AS shown more clearly in FIG. 3, tabs 49 extend from the side walls of crossbar 46- to a position where they may grazingly touch the opposing sides of the U-shaped filament wires 48 at the midpoint of the closed end. A metal tie-wire 50', such as tantalum for example, has a sufficient cross section and is attached at the ends 51 and 52 respectively to the cross bar 46 by conventional means, such as welding for example. Between ends 51 and 52, the flexible wire 50 is fastened, as at 53, to the closed ends of the U-shaped filament wires 48, at the midpoint, by conventional means, such as welding for example. Slack is left in the yieldable wire 50 to provide catenary curved portions 50a between the tie points 53 to avoid placing any stress on the filament wires 48 and to allow for differences in thermal elongation of the filament wires 48 during the operation of the tube.

When filament current flows through the U-shaped filament wires 48 heating them to incandescence, the filament wires 48 expand longitudinally and cause the closed ends of the respective filament wires 48 to extend further into the U-shaped cavity formed by cross bar 46 and extension tabs 49. Any tendency of the filament wires to move laterally toward the grid electrode will be restrained by the extension tabs 49 which will grazingly touch the sides of the closed ends of filament wires 48. Due to differences in the resistance of respective filament wires 48, the high value of current flowing through the filament wires will cause significant differences in voltage drop at the midpoints of the respective filament wires. Since these points of potential difference can be connected by each touching respective extension tabs 49, equalization currents will flow through the crossbar 46 from the point of higher potential to the point of lower potential. Any jarring of the tube during its operation can move one of the points of potential difference away from the respective extension tab 49. However, the equalization currents will not be interrupted because the points of potential difference are also connected by wire 50. Due to its flexibility and the slack in catenary curved por tions 50a between tie points 53, wire 50 follows the thermal elongation of the respective filament wires 48 in spite of differences in longitudinal expansion of the separate filament wires 48. Furthermore, wire 50 maintains an electrical connection between the midpoints of filament wires 48 and prevents any interruption of the equalization currents between points of potential difference. Therefore, the electrical noise, minute arcing, and vaporization of filament wires and extension tabs 49 that can be traced to the interruption of these equalization currents is thereby eliminated.

Thus, the foregoing description has disclosed a novel filament support structure which permits longitudinal expansion of U-shaped filament wires 48, restrains lateral movement thereof and maintains an electrical connection between their midpoints to avoid minute arcing and consequent vaporization caused by interruption of the equalization currents. It should be obvious to those skilled in the art that the disclosed filament structure can also be adapted for use with coaxial tubes having a cylindrical arrangement of parallel U-shaped filament wires extending longitudinally within the tube envelope. Other modiflcations will occur to those skilled in the art, such as having individual wires connecting the midpoints of the U-shaped filaments to the crossbar. Alternatively, the individual tie-wires can be replaced by resilient springs or resilient tangs. These and other modifications are not intended to limit the spirit and scope of this invention as outlined in the claims appended hereto.

What is claimed is:

1. A filament structure for an electron discharge tube comprising:

a linear array of parallel, U-shaped filament wires disposed longitudinally in an axial plane of the tube, said wires having a first end, a second end and a bight end, said wires being longitudinally expandable when heated by an electric current;

a first support member carrying the first end of the filament wires and adapted to conduct electrical current to and from the filament wires;

a second support member carrying the second end of the filament wires and adapted to conduct electrical current to and from the filament wires;

a crossbar fixedly supported in the same plane as the filaments, adjacent the bight ends of said filaments, and having a U-shaped channel therein open toward the bight ends of the filaments;

opposing extension tabs having one end attached to a wall of the U-shaped channel in the crossbar and disposed on opposite sides of the filament bight ends, at approximately the midpoint thereof, said tabs restricting lateral movement while permitting longitudinal movement of the filament wires into the U- shaped channel of the crossbar; and a a flexible wire attached at each end to the crossbar and intermediate the ends attached to the bight end of each filament at appoximately the midpoint and having slack portions between the attached portions, thus maintaining a constant connection between the crossbar and the midpoint of the filament wires to maintain equalization currents and avoid arcing resulting from the interrption of these equalization currents.

2. A filament structure for an electron discharge tube comprising:

an array of parallel, U-shaped filament wires disposed axially in the tube;

a first conductive support member attached to one of the terminal ends of each U-shaped filament wire;

a second conductive support member attached to the other terminal ends of the U-shaped filament wires;

a third conductive support member disposed in axial alignment with the filament array, spaced from the bight ends of the respective U-shaped filament wires and having opposing extended portions disposed on respective opposite sides of said bight ends whereby said filament wires are restrained from moving laterally;

and an integral, flexible conductor having respective portions thereof attached to respective bight ends of the U-shaped filament wires for maintaining a constant electrical connection between said bight ends of the filament wires. 3. A filament structure for an electron discharge tube comprising:

a linear array of parallel, U-shaped filament wires disposed longitudinally in an axial plane of the tube, each filament wire having a first terminal end, a second terminal end and a bight end;

a first support member attached to the respective first terminal ends of the filament wires;

a second support member attached to the respective second terminal ends of the filament wires;

an oblong, conductive member disposed in coplanar,

spaced relationship with the bight ends of the filament wires and having opposing extended portions disposed on respective opposite sides of the bight ends of the filament wires for restraining lateral movement thereof;

and a continuous flexible wire having responsive portions thereof attached to the bight ends of the U- shaped filament wires and having catenary curved portions "therebetween for permitting unrestricted longitudinal expansion of the filament wires while maintaining a constant electrical connection between the respective bight ends.

4. A filament structure for an electron discharge tube comprising:

References Cited UNITED STATES PATENTS 1/1932 Freeman et al 313--278 X 4/1932 Dijksterhuis 313279 X 6/1953 Corson et al 313278 3/1955 Shrader 3l3-299 X 7/1958 Shrader 313-278 X 1/1967 Freggens 313278 JOHN W. HUCKERT, Primary Examiner A. J. JAMES, Assistant Examiner US. Cl. X.R.

ii??? IIL'IED STATES PATENT OFFICE 54 by) CERMMQ TE 01* CORRECTION Patent No. 3,513,348 Dated May 19, 1970 Invencofls) Jacob A. Randmer and Erich C. Peter It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 19, change the word "responsive to espective 453M558 ARM f" Huifl 007 27 'f A Ir m1. Atteat:

mm M. Bea le m Atlesting Officer m E.

Commissioner of Patents ll1 Please amend above-referenced patent as follows: 

